Our earlier studies showed that DNA isolated from hemopoietic tissues of calves in whom aplastic anemia has been induced by a single dose of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) is abnormal with respect to its melting profile, buoyant density, susceptibility to hydrolysis by DNase and its ability to serve as template for DNA and RNA polymerases. When normal DNA is treated in vitro with DCVC and a lyase from bovine kidneys, the DCVC also assumes the same abnormal properties. These effects on DNA are caused by the interaction of an alkylating fragment formed from DCVC with the DNA. It has greatly reduced ability to form complementary complex with normal DNA and to hybridize with RNA. The interaction of the extremely reactive alkylating fragment produced from DCVC by lyase with various acceptors such as 4-(p-nitrobenzyl)-pyridine, p-nitrostyrene, glutathione will be studied in an attempt to isolate and characterize pure compounds.